Industrial source identification of polyhalogenated carbazoles and preliminary assessment of their global emissions

Polyhalogenated carbazoles (PHCZs) are emerging global pollutants found in environmental matrices, e.g., 3000 tonnes of PHCZs have been detected in the sediments of the Great Lakes. Recognition of PHCZ emissions from ongoing industrial activities worldwide is still lacking. Here, we identify and quantify PHCZ emissions from 13 large-scale industries, 12 of which previously have no data. Congener profiles of PHCZs from investigated industrial sources are clarified, which enables apportioning of PHCZ sources. Annual PHCZ emissions from major industries are estimated on the basis of derived emission factors and then mapped globally. Coke production is a prime PHCZ emitter of 9229 g/yr, followed by iron ore sintering with a PHCZ emission of 3237 g/yr. China, Australia, Japan, India, USA, and Russia are found to be significant emitters through these industrial activities. PHCZ pollution is potentially a global human health and environmental issue.

provide a visual comparison of different congener profiles from different industrial activities. 6. High concentrations of PHCZs in bottom residue liquid samples from organic chemical production were detected. However, the description about the information of production amounts of investigated chemicals on national scale or global scale is inadequate. I suggest supplementing basic information about the production amounts of investigated chemicals for better judging the potential importance of chemical production sources. 7. Could the authors provide a brief description about the temporal trend of PHCZ emissions from the important industrial sources? For example, recent five or ten years. %! ).0, $#& (/5"'25 .034,*+ 1-(/"'2! 9.Line 107: Change "detection rate" to "detection frequency" and throughout. 10. Line 148-149: The formation of PCDFs from the coupling reaction of chlorophenol and chlorobenzene under high temperature has been well studies. However, it is unclear whether PHCZs can be produced via similar pathways. Could the authors expand more on the possible formation pathways of PHCZs from these industrial activities? 11. As shown in Figure 1, high concentrations of PHCZs are emitted from coke production, secondary aluminum smelting, and municipal solid waste incineration. However, the emitting PHCZ concentrations from the three activities varied greatly from different plants. As for the same industry, are these plants used the same raw material and process for production? Could the authors explain why? What are the concentrations used for the estimation of the global emissions of PHCZs from these industries, since the emitting concentration of PHCZs varied greatly with different plants. 12. What is data source of the PHCZs in the environment presented in Figure 2? My understanding is that the figure analyzing the correlation of PHCZ congeners between fly ash and environmental samples. How can these results be used to interpret the occurrence of PHCZs in the environment?

Reviewer #3
This paper, for the first time, reports the concentrations of PHCZs in particulate matter (and bottom liquid) generated from industries. A total of 26 samples were collected from 26 plants of eight categories of industry, and 11 PHCZ congeners were analyzed in each sample. Efforts were made to examine the congener pattern, explore correlations between industrial emissions and environmental occurrence, and estimate the global industrial release of PHCZs. Such work is clearly important because, as the authors mentioned in L82-84 and I agree, that "current research on source identification is woefully inadequate, and knowledge to date does not support any reasonable explanation of the huge residues, wide distribution and complicated congener profiles of PHCZs in the environment". To this end, the necessity of conducting this work is justified. I also consider the experimental dataset valuable and would like to encourage its publication in an environmental journal. However, for the ambitious goal of providing a global assessment, the amount of work is too small, the conclusions are not solid, and the overall findings are too weak. For this reason, I do not recommend the publication of work in Nature Communications.

Major comments
Natural production of PHCZs is not the focus of this paper, but its importance must not be downplayed. In this paper, natural generations of PHCZs from fungi and volcano are mentioned in two sentences (L64-68), ignoring potentially significant (some are currently unknown) others. Based on this work, the total global emission of PHCZs from the eight industries is only about 10 kg/yr. How does this emission estimate compare with that for dioxins from the same industries? Such a low emission, if correct, could means that industrial emissions be insignificant compared with natural production, as far as total PHCZs concerned.
Where were all the samples collected? Is any from outside China? How are the samples (each from one filter bag used for 48 hr) representative even within China? Additionally, each industry was represented by only 1-4 samples. L461-462 mentions that 2 to 4 samples from each industry are "comparable to the open guidance published by some authorities", but these open guidelines are not provided. Within each industry, the reported concentrations differ by orders of magnitude. For example, global emissions of 8650 g PHCZs from coke production was estimated from only two COP samples which differ by 11 times in concentration (the first two rows in Table 1). Similarly, the only three samples of MSWI ranged from 0.1 to 29 ng/g ( Table 1). The averages were used in the estimations for global emissions in this paper. Such estimates bear huge uncertainties which diminish the differences among industries and make the conclusions in this paper (for example, "The biggest emitter among the investigated industries was COP" in L289) very doubtable.
The conclusion that "the congeners in the industrial emissions and environmental occurrences exhibit similar grouping" (L337-338) need more caution. The idea that positive correlations indicate cause-effect relationship is wrong. The section starting in L200 is simply a correlation analysis among congeners, it does not support the concluding statement "industrial activities are sources of PHCZs" (L216) "in the world" (L200). Similar comment can be made on the section starting in L218. Congener 1368-BCZ is believed to come from legacy dye industry, which was not involved in this work; thus L238-246 is not needed.
Throughout the paper, the concepts of congener and homologue are messed up. A total of 11 congeners were measured in this work, and they are in three homologues -chlorinated, brominated, and chlorobromo-carbazoles. The section starting in L162 has "congener" in the section title, but the content is mostly on homologues. In many places, the word "homologue" is used but individual congeners are focused.
The English is understandable, but lacks the concision and brevity. Some grammatical errors are present, especially towards the later section (e.g. Method). There are many redundant sentences and expressions in this paper. Significant efforts are needed to meet the criteria for technical writing, especially for publication in highly ranked journals.
Specific comments L43: References 2-5 appear to be randomly selected. Randomly picking of references should be avoided. Suggest removing Refs 1-5 or moving them to specific places in the paper where they fit more specifically.
L40-53: Given the focus of this paper is on PHCZ sources, the entire first paragraph about toxicity can be deleted for brevity and to avoid misunderstanding on the focus of this paper.
L60: Two papers should be cited along with Ref 25: https://dx.doi.org/10.1021/es503936u and https://doi.org/10.1021/acsestwater.2c00191. Please also replace "concentrations of 38 ng/g led to" with "a median concentration of 23.7 ng/g in surface grabs, and". The number 23.7 can be found in Li et al. 2022 Table S4. This number does not "lead" to the total load of 3354 tonnes in Table S6. L60-63: Delete these two sentences. Although nothing seems wrong, ambiguous words such as "huge" lower the quality of writing.
L96: Suggest ending the sentence after "liquids" and starting a new sentence "The results were examined for links and correlations with reported congener profiles in environmental samples, with the aim of identifying sources". SI-2 and SI-4 should be mentioned in the Result section, not here. L107-112: Suggest dividing this long sentence into two. One is "The industries included ….". Then, "Data obtained are shown in Fig. 1a".
L163-176: Suggest deleting these text "Emissions …. . So," which sound redundant and help nothing. L171-172: Suggest changing "some of them contained a large amount of PHCZs" to "the PM from some of these industries had high concentrations of total PHCZs". L195: The starting sentence is incorrect. This study is NOT the first discovering industrial sources of PHCZs. This paragraph is no use and should be deleted for brevity.
[Specific comments above are mostly editorial and for Introduction only.]  Please deleting half of the data which repeat the other half. In the caption, delete words "homologue". More importantly, are the original concentration data used for Spearman analyses in (b) from this study? Please specify the source of data in the caption. Also, the word "fly ash" is used here and in Supplementary Information-2. Do you consider i-PM and fly ash the same thing? Fig 5b: The unit is "g/t", which is not easily understood. Suggest adding explanations in the caption, "grams of i-PM emitted per tonne of production capacity", if correct. The unit for the numbers is "g" (gram), which is incorrect. Please clarify it is grams per year, per day, or per hour? If year, please add "annual" in the caption. Also, which year should be specified -2010 or 2020 or another? Table 1: All concentrations are reported with precision to 1 pg/g. Some larger numbers have six significant figures! Please re-consider the precision level of the data reported in this paper.

Reviewer #1:
General comments: Polyhalogenated carbazoles (PHCZs) are structural similar to that of polychlorinated dibenzofurans (PCDFs) that attracting global concerns on their sources and control. The toxicity of PHCZs is like PCDFs with high carcinogenicity. However, compared to PCDFs, very little attention was given to the potential sources of PHCZs. The authors conducted many monitoring activities of polyhalogenated carbazoles in particle matters collected from a big size of industrial plants on real full-scale. This study provides essential new data for recognizing important sources of PHCZs and implementing their controlling strategy. I recommend minor revisions before it could be accepted.

Response:
We greatly appreciate your positive comments about the importance of our monitoring data and the constructive suggestions provided. We have carefully revised our manuscript based on your comments.
Detailed responses to your comments are provided below.

Comment (1):
I suggest adding a figure in the supplementary information to display the molecular structure of polyhalogenated carbazoles with numbering of carbon atoms, as well as the structures of the detected congeners in the study. It could help to easily understand their congener profiles.

Response:
Thank you for your comment. We have added the molecular structure of polyhalogenated carbazoles The authors compared the concentrations of PHCZs in different industrial sources and make reasonable explanations for most of the studied industrial sources. However, the low concentrations of PHCZs in lead smelting and coal fired power plants were not explained. The authors should discuss the possible reasons of the low concentrations. In addition, the authors should explain why high concentrations of PHCZs in PM from coke production?

Response:
Thank you for your comment. PHCZs are unintentionally produced persistent organic pollutants (POPs), which might share a similar formation mechanism with that of other POPs, such as dioxins and polychlorinated naphthalenes (PCNs). Secondary lead smelting processes generate much lower concentrations of dioxins and PCNs than other secondary non-ferrous metal smelting processes 1 . Previous studies indicated that lead has less catalytic activity than copper and zinc for the formation of PCDD/Fs during smelting processes 2 . Sulfur in coal can inhibit the formation of dioxins during processes of coal fired power plants 3 . A similar mechanism might be the reason for the low concentrations of PHCZs from coal-fired power plants. Coke production generates coal tar as an important by-product, of which carbazole constitutes 0.5% to 1.8% 4 . The halogenation of carbazole during coke production might lead to the high concentration of PHCZs, which is perhaps why we observe high concentrations of PHCZs in i-PM samples from coke production. The above explanations have been added to the revised manuscript.

Comment (3):
What are the potential release pathways for organic chemical plants? Is it possible for PHCZs to enter environment by waste water, gas diffusion, solid or liquid residues like those of dioxin emissions? Please add relevant discussion.

Response:
Thank you for your comment. The bottom liquid samples collected in our research require further treatment, such as incineration as hazardous wastes. However, we found considerable PHCZs in sediment samples from Yaer Lake, an area suffering from historical wastewater discharge from chemical plants.
The results indicated that wastewater is a potential PHCZ release pathway in organic chemical production.

Comment (5):
In the Supplementary Information 16, relative effect potencies (REPs) of PHCZs based on the structure-dependent induction of cytochrome P450 1A1 mRNAs in MDA-MB-468 breast cancer cells were not listed. Please list those REPs of PHCZ congeners that adopted for TEQ calculations.

Response:
Thank you for your comment. Riddell

Comments (6):
Supplementary Information 3. The information in this section, such as Production Equipment/Scale, Raw Materials should be checked and confirmed. Description about Coke Oven Chamber in the Table   seems to be incorrect.

Response:
Thank you for your comment. We checked and confirmed the Industry Coefficient Manual and updated the emission coefficients of particulate matter for these industries, which has been added to supplementary information 9.  This is a timely report on the investigation of anthropogenic source of polyhalogenated carbazoles (PHCZs), a new class of emerging contaminants with considerable environmental loads and risk. Although increasing studies have suggested that PHCZs in the environment could be attributable to anthropogenic and natural sources, the formation/emission pathways are still inclusive. This study for the first time investigated the emissions of many previously unrecognized sources of PHCZs from industrial activities.

Supplementary
The emissions of PHCZs from 12 large-scale industries were identified and evaluated. The presented source emission data is very abundant and important for interpretating the widespread occurrence of PHCZs in various environments. I recommend to accept this manuscript for publication after minor revisions or explanations.

Response:
Thank you for your positive comments about the timeliness of our work. The suggestions are also very helpful to improve this first investigation of PHCZs emitted from these industrial sources. We further expanded the investigated industrial plants from 26 factories to 122 factories, which allows for a more comprehensive assessment of PHCZ emissions in various industries. Furthermore, we have also determined the emissions of PHCZs from a new source, iron ore sintering, which improves the overall understanding of industrial PHCZ pollution. We have revised the manuscript based on these suggestions.
Detailed responses to the specific comments are listed below.

Comment (1):
Did the authors characterize the fine particle matters collected from the large-scale industrial sources?
I suggest providing a few examples (such as 1-3 samples) to display the basic properties of the particle matters from industrial sources, such particle size.

Response:
Thank "EAF (electric arc furnace steel)" should be changed to "EAF (electric arc furnace for steel-making)".

Response:
Thank you for your comment. We have changed "electric arc furnace steel" to "electric arc furnace for steel-making" in the revised manuscript at line 77.

Comment (3):
Eleven PHCZ congeners were detected. There are more congeners than detected in this manuscript.
Could the authors further explain why those eleven congeners were selected in this study?

Response:
Thank you for your comment. The PHCZ congeners widely detected in the environment are the 11 PHCZ congeners selected for this study. PHCZs in drinking water was reported 8 . Our research is aimed at exploring more potential industrial sources. With this goal, we selected the 11 PHCZs widely detected in the environment to explore the relationship between PHCZs from industrial sources and PHCZs accumulated in the environment and the possible industrial contribution to environmental PHCZ pollution. In our revised manuscript, we discuss why the 11 congeners were selected.

Comment (4):
The The REFs of PHCZs are shown below and also in supplementary information 13.

Supplementary Information 13
The relative effect potencies (REPs) of PHCZs 5

Comment (6):
High concentrations of PHCZs in bottom residue liquid samples from organic chemical production were detected. However, the description about the information of production amounts of investigated chemicals on national scale or global scale is inadequate. I suggest supplementing basic information about the production amounts of investigated chemicals for better judging the potential importance of chemical production sources.

Response:
Redacted Editorial Note: Parts of this Peer Review File have been redacted as indicated to remove third-party material where no permission to publish could be obtained.
Thank you for your comment. According to data released by the International Chemical Industry Association, the global production of chemicals in 2020 reached 529 million tonnes, the global production of vinyl chloride in 2019 was 48 million tonnes, and the global production of chlorobenzene in 2016 was approximately 3 million tonnes. We have added relevant discussions to our revised manuscript 21 .

L321-323:
There is also possible extra emissions through OC, which produces 529 million tonnes of chemicals in 2020 21

Comment (7):
Could the authors provide a brief description about the temporal trend of PHCZ emissions from the important industrial sources? For example, recent five or ten years.

Response:
Thank you for your comment. In our research, the global PHCZ emission depended on the production output of these industries. However, the production output of important industries remains stable in the past few years. For example, global production outputs of electric arc furnace for steel-making were 563,  Therefore, we considered that the temporal trend of PHCZ emissions is similar to the temporal trend of production output in each industry. However, we agree with the reviewer in that evaluating the historical emission and accumulation of PHCZs over a long timeframe is necessary. We have highlighted this issue in the conclusion to call for more attention. year Thank you for your comment. We have changed this in the revised manuscript. The modified content is as follows: Line 52-53: Fungal activity can be a natural PHCZ source. Mumbo et al. 22 confirmed that in the presence of H2O2 and Cl-/Br-, fungi can bio-transform carbazole (CZ) to PHCZs.

Response:
Thank you for your comment. We have made this change in the revised manuscript. The modified content is as follows:

Response:
Thank you for your comment. The differences in raw materials might be the reason for the variability.
A previous study reported that raw materials play a significant role in the amount of generated PCDD/Fs.
For example, the raw material of secondary aluminum smelting, aluminum scrap, can be scrapped in different application scenarios, leading to differences in halogen and carbon contents. Therefore, there might be uncertainty in industrial field studies.
However, we tried to reduce the uncertainty for our revised manuscript. We made efforts to expand the number of investigated plants from 26

Comment (12):
What is data source of the PHCZs in the environment presented in Figure 2? My understanding is that the figure analyzing the correlation of PHCZ congeners between industrial particle matters and environmental samples. How can these results be used to interpret the occurrence of PHCZs in the environment?

Response:
Thank you for your comment. In this research, the data are from previous environmental investigations of PHCZs. We have added descriptions and details to supplementary information 3. We checked the figures and made some correction. Some figures have been added to describe the correlations of PHCZ congener concentrations in each industry and to present the emission features of each industry.
The same analysis was also conducted for PHCZs in soil and sediment, two environmental matrices containing PHCZs, which combined with congener concentrations was used for source identification of specific congeners. We have provided an interpretation of these results in the revised manuscript. Information 3). plants in one single field study is very large, especially for PHCZs, which lack industrial field data. We sincerely hope the reviewer understands the practical difficulties when conducting industrial field studies.

Supplementary Information 3) was conducted to understand the source and environmental characteristics of PHCZs (data processing in Supplementary Information 7). As shown in Fig 3 (red and blue indicate positive and negative correlations, respectively), certain congeners display a strong positive correlation with other congeners in SAl, MSWI, and CK. However, weak correlations with other congeners could be seen for 3-CCZ and 3-BCZ in
We also changed the title to 'Polyhalogenated carbazoles: Identification of new sources and estimation of global emissions' in the revised manuscript. Detailed responses to specific comments are shown below.
Additions and revisions are highlighted in the revised manuscript.

Comment (1):
Natural production of PHCZs is not the focus of this paper, but its importance must not be downplayed.
In this paper, natural generations of PHCZs from fungi and volcano are mentioned in two sentences (L64-68), ignoring potentially significant (some are currently unknown) others. Based on this work, the total global emission of PHCZs from the eight industries is only about 10 kg/yr. How does this emission estimate compare with that for dioxins from the same industries? Such a low emission, if correct, could means that industrial emissions be insignificant compared with natural production, as far as total PHCZs concerned.

Response:
Thank you for your comment. As the reviewer mentioned, this study is focused on the industrial emissions of PHCZs, not the natural production of PHCZs. It was believed that the discovery and estimation of PHCZs from several important industrial activities, first conducted in the study, could greatly contribute to filling the recognition gap of emission sources of PHCZs.
We also fully agree with the reviewer in that natural production contributes to the occurrences of PHCZs in the environment, which has been previously reported, and we have pointed this out in the  Table 1). Similarly, the only three samples of MSWI ranged from 0.1 to 29 ng/g ( Table 1). The averages were used in the estimations for global emissions in this paper. Such estimates bear huge uncertainties which diminish the differences among industries and make the conclusions in this paper (for example, "The biggest emitter among the investigated industries was COP" in L289) very doubtable.

Response:
Thank you for your comment.

Information 2
As an industrial field study, online monitoring of PHCZs has not been achieved, although online monitoring of normal pollutants (such as NOx and SOx) has been conducted. Analysis of PHCZs requires a series of complex analytical procedures. The cost required to identify and quantify PHCZ congeners is also relatively high owing to use of 13  To our best knowledge, the current sample size with 122 investigated industrial plants in one single field study is large, especially for PHCZs, which lack industrial field data. Therefore, we sincerely hope the reviewer understands the practical difficulties when conducting industrial field studies.
L359-361: In total, 122 industrial plants from 13 industries were included in this study. This comprehensive field investigation enables source identification and emission estimation of POPs in one single study 23 .

Comment (3):
The conclusion that "the congeners in the industrial emissions and environmental occurrences exhibit similar grouping" (L337-338) need more caution. The idea that positive correlations indicate cause-effect relationship is wrong. The section starting in L200 is simply a correlation analysis among congeners, it does not support the concluding statement "industrial activities are sources of PHCZs" (L216) "in the world" (L200). Similar comment can be made on the section starting in L218. Congener 1368-BCZ is believed to come from legacy dye industry, which was not involved in this work; thus L238-246 is not needed.

Response:
Thank you for your comment. We have deleted the sentence "the congeners in the industrial emissions and environmental occurrences exhibit similar grouping" and have given a conclusion with more caution in L190-218. We have checked the correlation analysis and updated our conclusions, which focus more on the features of PHCZs through these investigated industries. The sentences that the reviewer pointed out have been rewritten in a more cautious way.

Comment (4):
Throughout the paper, the concepts of congener and homologue are messed up. A total of 11 congeners were measured in this work, and they are in three homologues -chlorinated, brominated, and chlorobromocarbazoles. The section starting in L162 has "congener" in the section title, but the content is mostly on homologues. In many places, the word "homologue" is used but individual congeners are focused.

Response:
Thank you for your comment. We have made corrections accordingly in the revised manuscript. The English is understandable, but lacks the concision and brevity. Some grammatical errors are present, especially towards the later section (e.g. Method). There are many redundant sentences and expressions in this paper. Significant efforts are needed to meet the criteria for technical writing, especially for publication in highly ranked journals.

Response:
Thank you for your comment. We have polished our manuscript using a professional editing company recommended by Springer Nature and ACS. Certificate of editing is displayed below.

Comment (6):
L43: References 2-5 appear to be randomly selected. Randomly picking of references should be avoided. Suggest removing Refs 1-5 or moving them to specific places in the paper where they fit more specifically.

Response:
Thank you for your comment. We have deleted the references accordingly.

Comment (7):
L40-53: Given the focus of this paper is on PHCZ sources, the entire first paragraph about toxicity can be deleted for brevity and to avoid misunderstanding on the focus of this paper.

Response:
Thank you for your comment. We have deleted the paragraph about toxicity.

L39: PHCZs, as emerging dioxin-like compounds (DLCs) 30
Comment ( 2022 Table S4. This number does not "lead" to the total load of 3354 tonnes in Table S6.

Response:
Thank you for your comment. We have added the references at L60 (L49 in revised manuscript) and changed '26 PHCZs with concentrations of 38 ng/g led to an estimated > 3000 tonnes in the sediments' to '26 PHCZs with a median concentration of 23.7 ng/g in surface grabs, leading to an estimated >3000 tonnes in sediments' at L59 (L47-48 in revised manuscript).

L48-51: An investigation of the pollution status of the Great Lakes revealed the existence of 26
PHCZs with a median concentration of 23.7 ng/g in surface grabs, leading to an estimated >3000 tonnes in sediment, which is orders of magnitude greater than those of PCBs and PBDEs 29,31,32 .

Comment (9):
L60-63: Delete these two sentences. Although nothing seems wrong, ambiguous words such as "huge" lower the quality of writing.

Response:
Thank you for your comment. We have deleted the two sentences.

Response:
Thank you for your comment. The comma in 'current research on source identification is woefully inadequate, and knowledge to date' has been removed following editing.

Response:
Thank you for your comment. We have deleted these statements.

Response:
Thank you for your comment. We have changed 'particulate matters' into 'particulate matter' throughout the paper.

Comment (13):
L96: Suggest ending the sentence after "liquids" and starting a new sentence "The results were examined for links and correlations with reported congener profiles in environmental samples, with the aim of identifying sources". SI-2 and SI-4 should be mentioned in the Result section, not here.

Response:
Thank you for your comment. We have modified these sentences and marked them in the revised manuscript.

Response:
Thank you for your comment. We have modified these sentences and marked them in the revised manuscript.

Response:
Thank you for your comment. We have deleted these sentences.

Comment (16):
L171-172: Suggest changing "some of them contained a large amount of PHCZs" to "the PM from some of these industries had high concentrations of total PHCZs".

Response:
Thank you for your comment. We have changed this expression.

Comment (17):
L195: The starting sentence is incorrect. This study is NOT the first discovering industrial sources of PHCZs. This paragraph is no use and should be deleted for brevity.

Response:
Thank you for your comment. We have deleted this paragraph.

Response:
Thank you for your comment. We agree with the reviewer's conclusion and have added a brief explanation at L150-152. from this study? Please specify the source of data in the caption. Also, the word "fly ash" is used here and in Supplementary Information-2. Do you consider i-PM and fly ash the same thing?

Response:
Thank you for your comment. We have modified the figure as suggested. The citations of environmental investigations have been added to the supplementary information 3. In our research, we obtained SEM images of our samples and the results indicated the particle diameters are less than 2.5 !m.
Relevant results are provided in Supplementary Information 11.

Response:
Thank you for your comment. We have modified the caption accordingly and marked it in the

Minor comments and suggestions
Title: Suggest changing "new" to "industrial". It might also be better to replace "estimation" with "preliminary assessment".
L53: "Cl-/Br-" is confusing. Do you mean chloride and bromide ions, or their ratio, or something else?
L59: Refs 17 and 18 are not considered "recently". Suggest deleting "as well as …. materials", and moving statements about indigo dye and photoelectric materials to later sentences.
L60: The word "However" is not needed and confusing. Also, based on how many and which references, 3,6-BCZ is considered low in environmental media?
L86: Move "for the first time" to immediately after "mapped" and before the comma. This study is certainly not the first one using emission factor method.
L92: Suggest adding "11" as a subscript for the sigma in all "sigmaPHCZs" in this paper, to indicate clearly how many congeners are included. This term should be used whenever appropriate; for example, replace "total PHCZs" (L233) and "11 PHCZs" (L240) with "sigma11PHCZs".
L101: Change "can be obtained from i-PM" to "were found in i-PM samples".
L154-158: Strongly suggest deleting this sentence, which is irrelevant to this study.
L164: Change "could not be" to "were not".
L167: Suggest changing "occupy a larger area with proportions more than 70% in" to "count for more than 70% in samples from".

Response:
We greatly appreciate your recognition on the representative of the investigated industrial sources and the discussions in our revised manuscript. Your constructive and insightful suggestions and comments play a strong role in the improvement in our revised manuscript. Thanks again!

Reviewer #3:
General comments: Compared with the original version, this revision is a significant improvement.

Response:
We sincerely appreciate your recognition on the improvement in our revised manuscript. Thanks for the constructive comments. We have carefully revised our manuscript based on your comments. negatively affect data interpretation and future study designs.

Response:
Thanks for your reviews and insightful comments. We have reviewed all the findings in the references in this manuscript to avoid exaggerative generalization.
Detailed revisions are highlighted in revised manuscript and shown below.